Jove said:
Apple does it all the time for their Apps.
Not all the time, there are the two big debacles I can think of off the top of my head.
Pokemon Yellow, which didn't work. At all.
http://www.escapistmagazine.com/forums/read/7.351547-Counterfeit-Pokemon-Game-Tops-App-Charts
Several Super Mario copy pastes.
http://www.escapistmagazine.com/news/view/109681-Apple-Approves-Blatant-Mario-Rip-Off-for-App-Store
http://www.escapistmagazine.com/news/view/119631-iOS-Game-Takes-Mario-Knockoffs-to-The-Next-Level
I'm not trying to defend Valve, just making the point that even Apple doesn't do a very good job checking either and the above examples are actually in some ways worse than the current. The hope is that this entire thing will make Valve change their policy and take the game down.